1. Field of the Invention
The present invention generally relates to circular saw blades used to cut a two-tier expansion groove in a concrete surface or the like and, more particularly, is concerned with features incorporated in such blades which reduce wear, increase structural integrity, and prolong useful life of the blades.
2. Description of the Prior Art
It is common practice to cut two-tier grooves in concrete surfaces or the like in order to provide expansion joints therein. The grooves are filled with a compression sealant of neoprene or other similar synthetic rubber-like material which allows the grooves to function as expansion joints in response to temperature-induced expansion or contraction. Until recently the two-tier groove has been made in two cutting passes. In the initial pass, a first narrow groove is cut having the maximum desired depth of the two-tier groove. In the final pass, a second wider groove is cut into the surface superimposed over the first narrower groove but to a lesser depth than the first groove.
More recently, in U.S. Pat. No. 4,930,487 to Younger, a design of a circular saw blade has been proposed for cutting the two-tier groove in a single pass. The saw blade of this patent includes a circular core of uniform thickness having a plurality of outer cutting segments secured to circumferentially spaced support sectors defined about the periphery of the blade core and a plurality of inner cutting segments disposed in openings and secured to support lands defined in the blade core between the periphery and the center of the blade. In order to cut the two tier groove, it is necessary that the outer cutting segments be wider than the blade core and that the inner cutting segments be wider than both the outer cutting segments and blade core. In one pass of the saw blade, the outer cutting segments will cut the deeper and narrower tier of the groove, whereas the inner cutting segments will cut the shallower and wider tier of the groove above the deeper narrower tier of the groove.
For such applications, it is common practice to continuously flush the cutting area during the cutting operation with a fluid coolant in order to keep the blade as cool as possible. The coolant also serves to flush loose rock-like material, spent abrasive, and the like from the cutting site, all of which in combination with the coolant is generally referred to in the art and throughout the subject application as "swarf".
Although the design of the circular saw blade of the Younger patent represents a step in the right direction toward achieving the cutting of a two-tier expansion groove in a single pass operation, nonetheless there are certain drawbacks with the design. The first drawback is that swarf tends to flow in a path that contacts and causes abrasion and erosion of the blade core in a manner which is commonly referred to as "undercutting". The undercutting occurs at core portions located adjacent to and radially inwardly from where the outer and inner cutting segments are attached to the blade core because the lateral portions of the outer and inner cutting segments extend beyond opposite surfaces of the core and tangentially intersect with the swarf flow path. Such undercutting of the blade core can significantly reduce the life of the blade necessitating its early replacement. The second drawback is that the blade core is of substantially uniform thickness. Given the greater width of the inner cutting segments than the outer cutting segments for cutting the wider upper tier of the groove, there is inadequate structure in the blade core for attaching the inner cutting segments thereto in a way which will withstand the forces imposed on the inner cutting segments during cutting of the upper tier of the groove.
Consequently, a need exists for improvements which will reduce undercutting of the blade core and increase the structural integrity of the blade core so as to allow for the employment of the circular saw blade over a longer normal useful life.